(CNN) -- Democrats say they have a "dream team" of Sens. Hillary Clinton and Barack Obama but they might be looking at a nightmare if superdelegates have to determine which one will be at the top of the ticket.

Sen. Barack Obama leads in the overall delegate count, but the race is close.

Usually the superdelegates are an afterthought -- the nominee normally emerges before the National Democratic Convention by winning enough delegates in the caucuses and primaries to capture the nomination.

But this year, Obama and Clinton are running such a tight race that after millions of votes and months of campaigning, neither candidate is expected to have the 2,025 delegates needed to seal the nomination before the August convention.

Superdelegates -- made up of governors, senators, house members and various other party officials or members -- are also known as "unpledged" delegates.

They are free to choose the candidate they like, while pledged delegates are assigned in primaries and caucuses.

Many superdelegates pledge allegiance to a candidate well before the party convention, but they can change their minds. Superdelegates make up around 20 percent of the total delegates.

The idea of a select group determining the outcome doesn't sit well with everyone.

"It's not the most democratic way of doing things," said Maine superdelegate Sam Spencer.

At least two organizations have launched petition drives to have the convention reflect how the vote went in primaries and caucuses.

MoveOn.org, which has endorsed Obama, has a petition posted that says, "The Democratic Party must be democratic. The superdelegates should let the voters decide between Clinton and Obama, then support the people's choice."

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The group is trying to get 300,000 signatures by Monday before running the petition as an ad in USA Today.

Similarly, Democracy for America, headed by Democratic National Committee Chairman Howard Dean's brother Jim, has a petition that warns the nominee "must be chosen by Democratic voters, not by backroom deals of the party elite."

Obama leads in the overall delegate count and among pledged delegates, but Clinton has more superdelegates supporting her.

Clinton has 235 superdelegates backing her compared to 160 for Obama.

As for the other nearly 400 members, they're either undecided or keeping their decision private for now.

The superdelegate setup was established in 1982 to bring more moderate Democrats back to conventions, where their attendance had been dropping since the 1950s, and to reflect the party's mainstream more accurately.

"[Superdelegates] are the keepers of the faith," said former San Francisco, California, Mayor Willie Brown.

"You have superdelegates because this is the Democratic Party. You don't want the bleed-over from the Green Party, the independents and others in deciding who your nominee will be."

The first campaign to benefit from the roles of superdelegates was that of former Vice President Walter Mondale in 1984. His 1984 campaign went into the party convention with too few delegates to secure the nomination against the campaigns of former Sen. Gary Hart and Jesse Jackson. Mondale had received more votes, but Hart had won more states.

Mondale was able to line up the superdelegates going into the convention and avoid a fight on the convention floor.

The Obama and Clinton camps are trying to do the same thing by actively encouraging the superdelegates to pledge to their side.

While divided over which candidate to support, Democrats are largely agreed the battle over delegates needs to be resolved without a sense that superdelegates are making a decision that opposes what voters want.

"There has to be some agreement between the Clinton and Obama campaigns as to how to handle it," New York Sen. Chuck Schumer, a prominent supporter of her campaign, said Sunday.

"We need to win in November and if one side tries to shove down the throats of the other side any rule, so that ... all of her or his supporters walk away upset, we will lose." E-mail to a friend

CNN's Campbell Brown, John Helton, Robert Yoon and Ed Hornick contributed to this report.